Power wise, Uro seems to be the most powerful due to his draw/ramp/life package.
Polukranos whom I already started a thread here, noted that he could be a repeatable creature killer once you provide protection and growth, all the while being a perfect sac fodder due to its size.
Kroxa's ability to group-slug at low cost is valuable, and he will likely go into a discard-centric deck or as a support in Grixis, and B/R never lacks a way to drop things into the GY (and Squee can return again and again!). However, I am not sure if one card (even if from everyone) is good enough, compare to Uro's universal effect and Polukranos's potential two-hit kill.
After testing, I noticed that I tend to cast both titans TWICE from command zone before sending them to the graveyard waiting to escape. Uro is a given since his ability makes each recast that much easier, Kroxa would require extra support and vice effect. Polukranos being Golgari gives him permanent destructions the other two lack.
I will make decks for all of them, that's for sure. I don't shay away from powerful but costly effects.